Base stations for communications operate at power levels on the order of many watts. Implementations of duplex filters located in base stations having a single antenna for both transmit and receive operations typically include air cavity duplex filter designs. Such filter designs include multiple resonators which when tuned properly operate in concert to achieve filter performance needs. Resonators are coupled to each other through parasitic and other paths. Tuning a given resonator can affect the operation of other resonators because of cross coupling inherent in the design of such filters.
Air cavity filters are cost effective to manufacture using well known machining techniques. Air cavity filters can also handle high power levels. However, there are specialized applications where the size and weight of air cavity filters is prohibitive. In the interest of mining scarce bandwidth resources, base station serving areas are becoming much smaller. In fact, customers and operators prefer to minimize the footprint and mounting constraints for base stations. As a result, filters in the base stations need to be smaller.
Planar techniques, such as for example microstrip techniques, stripline techniques or other printed techniques, enable low cost design of printed filters, including ceramic filters with printed surfaces. Many types of printed planar filters or ceramic multi-resonator filters often have lot-to-lot or device-to-device performance variation that can cause performance to fall outside of specified tolerances. This may include shrinkage of the ceramic block, inaccuracies in the ceramic mixture, inaccuracies in the furnace firing, thickness variation of the plating, and errors in pattern positioning each have a large effect on part-to-part and lot-to-lot filter performance. Moreover, each filter must be manually tuned resulting in a laborious and expensive process requiring significant knowledge of the art.
Separately, printed planar filters or ceramic multi-resonator filters can be difficult to design particularly when the design incorporates both bulk field resonances and high E-field couplings. The design process for these filters initially involves simulating the filter resulting in an accurate prediction of the final filter performance. However, this does not provide much instruction on how to achieve the final performance. Conventional methods require the designer to use a laborious and expensive process that requires significant knowledge of the art to design the printed pattern that will yield the originally simulated performance.
What is needed is an automated tuning, design and manufacture method enabling low cost, precision manufacture of printed filters.
What is also needed is a faster and more stepwise approach to tuning filters, during production and post production in the field, which allows a less-trained technician, or an automated robotic system to tune each filter into compliance in a fast and cost-effective way.
What is further needed is a stepwise approach to design filters which guide the designer, technician, or computer in a way that causes the printed pattern to converge to the appropriate final design.